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Elevator System (LLD)

Problem Statement

Design and implement an Elevator System that can handle multiple requests, move between floors, and manage direction and elevatorState efficiently.

Requirements

  • Multiple Elevator: The system manages multiple elevators.
  • Request Handling: The system can handle requests to move to specific floors in a given direction (UP/DOWN).
  • Direction Management: The elevator maintains and updates its current direction (UP, DOWN, IDLE).
  • State Management: The elevator tracks its current floor, direction, and pending requests.
  • Efficient Movement: The elevator processes requests in an efficient order (e.g., all UP requests, then all DOWN requests).
  • Extensibility: Easy to add more elevators or advanced scheduling algorithms.

Core Entities

  • Elevator: Represents the elevator, manages its elevatorState, direction, and request queue.
  • ElevatorController: Handles incoming requests and delegates them to the elevator.
  • Request: Represents a request to move to a specific floor in a given direction.
  • Direction (enum): UP, DOWN, IDLE.

Class Design

1. Elevator

  • Fields: currentFloor, direction, List requests, isMoving, etc.
  • Methods: addRequest(Request), move(), openDoor(), closeDoor(), processNextRequest(), getCurrentFloor(), getDirection(), etc.

2. ElevatorController

  • Fields: Elevator elevator
  • Methods: requestElevator(int floor, Direction direction), step(), etc.

3. Request

  • Fields: int floor, Direction direction

4. Direction (enum)

  • Values: UP, DOWN, IDLE

UML Class Diagram

Example Usage

ElevatorController controller = new ElevatorController();
controller.requestElevator(5, Direction.UP);
controller.requestElevator(2, Direction.DOWN);

// Simulate elevator steps
for (int i = 0; i < 10; i++) {
    controller.step();
}

Demo

See ElevatorSystemDemo.java for a sample usage and simulation of the elevator system.

Extending the Framework

  • Add multiple elevators: Create a list of Elevator objects and update the controller logic.
  • Advanced scheduling: Implement algorithms for optimal elevator assignment.
  • Add features: Such as maintenance mode, emergency stop, or floor elevatorDisplay.